Data release to the US ROSAT Data Archive has been continuing. As of this
writing, the US data archive contains data released by the US through August
1995 as well as data released by MPE through June 1995. A major effort is now
underway to automate the release of data to the public archive, which should
ensure more timely release and availability of ROSAT data.

II. Release of Reprocessed Data

Observations made in the early part of the ROSAT mission are presently being
re-processed with the most up-to-date version of SASS and redistributed to the
principal investigators. The PIs retain data rights to the reprocessed data
for a period of 6 months, after which time the data are released to the ROSAT
archive. The first set of reprocessed data will become publicly available
sometime in the fall of 1995. Archive users should note two important
points:

the reprocessed data will REPLACE the earlier versions of the processing.
This means that the original (REV0) version of the dataset will no longer be
readily available from the ROSAT archive.

the reprocessed data will enter the archive in RDF FITS format, not in the
REV0 fits format previously used, independent of whether the data were
reprocessed at MPE or GSFC.

At the present rate of data reprocessing, it is expected that reprocessing will
be completed by March 1996.

III. The ROSAT RESULTS Archive

A. Introduction

Probably the most important development to impact ROSAT archive users is
construction of the ROSAT Results Archive, which began this spring. As users
of the data archive know, certain ROSAT data products ("results") were deemed
potentially unreliable and were withheld from public distribution pending
reprocessing and data screening. "Results" include background maps, extracted
source lists, source spectra and source lightcurves. The RESULTS ARCHIVE is
now being developed to make these "results" available in a sensible way to the
general public so as to allow access to a reliable source list and to alert the
archive user to potential problems in derived counting rates, spectra, etc.
The ROSAT RESULTS ARCHIVE is being constructed by joint effort of the data
centers in Germany, the UK and the US. Each site will be involved in the
flagging of the data and releasing the data to the public.

B. Phase 1 - Results Flagging and the Q-SOURCE file

In this initial stage (Phase 1), most of the effort is being directed toward
construction of a reliable source list. The source list we produce will
represent a summary of detected source characteristics for ROSAT pointings with
the PSPC and HRI. Similar lists for the PSPC have been recently released (the
"WGACAT" list produced by White, Giommi and Angelini and the "ROSATSRC" list
produced by Voges et al. at MPE). The aim of the ROSAT RESULTS ARCHIVE effort
is to produce a reliable list, i.e., a list in which each source has an
indicationas to whether the derived source characteristics (position,
brightness, etc.) are deemed reliable or not.

To do this, the source lists produced by SASS processing are screened by
automatic and visual methods and obvious problems are flagged. The SASS source
lists, along with the flags, are copied to a "quality-screened" source file
which is then released to the public. We emphasize that this
"quality-screened" source file (sometimes called the Q-SOURCE file) contains
ALL the original SASS data in addition to quality flags and other useful
information generated as part of the data flagging. The FITS version of the
Q-SOURCE file is named according to the following convention:

r<instrument><ror><pointing>_qsrc.fits,

where <inst> = p, f, or h is the instrument, <ror> is the 6-digit
ROSAT observation request number, and <pointing> the 3 character pointing
extension (N00, A01, etc.) Users will have access to the Q-SOURCE file from the
US archive via the usual methods (anonymous ftp from legacy.gsfc.nasa.gov or by
e-mail request to the NDADS ARMS server).

Data flags are divided into 2 types: "Sequence Flags" which pertain to an
entire sequence and "Source Flags" which apply to individual sources in a data
sequence.

Sequence Flags are logical flags which indicate to a user whether any of a
number of conditions are thought to exist for a given sequence. Sequence flags
are stored as logical header keywords in the first binary table extension
header in the Q-SOURCE FITS file. Table 1 lists the keyword names and the
condition which triggers a "True" value. If a condition is not thought to
exist for a given sequence, the keyword value is set to "False".

ASP_SUSP obvious aspect problems (sources appear
multiple or have obvious ellipticity)
EXT_EMIS presence of extended emission over most of the field
FALS_DET one or more detected sources deemed false
DEFERRED data screening not done
MISS_SRC one or more obvious sources not detected by SASS
BKG_SUSP Field background may be incorrect (due to inclusion of
high background intervals or extended emission)
NO_SRC source list is missing (no sources detected by SASS or
source detection stopped)

Source Flags are logical flags which indicate to a user whether any of a number
of conditions are thought to exist for a given source in a given sequence.
Each source has a set of flagged quantities. Source flags are stored as
logical columns in the first binary table extension header in the Q-SOURCE FITS
file. Table 2 lists the column names and the conditions which trigger a "True"
value. If a condition is not thought to exist for a given source, the column
value is set to "False".

As part of the HRI data flagging, images with smaller pixel scales (5 arcsec/
pixel and 2 arcsec/pixel vs. 8 arcsec/pixel image produced by SASS) are
generated. These images better sample the HRI point-response function and
therefore offer potentially more spatial information than the standard SASS
image. Presently we plan to release these images to the public HRI archive so
as to allow users access to these images as well as the standard SASS image.
In addition to the above products, a list of obvious sources which were not
detected by SASS will also be compiled.

C. Phase 2 and beyond

Additional data products and software tools are needed if users are to take
full advantage of the wealth of data in the ROSAT archive. These products and
tools include:

1) the merging of add-on and follow-on observations to maximize mean exposure
in each field;
2) unique identification of each detected source and correlating with known
sources from other catalogues;
3) extraction of upper limits from pointed data;
4) extraction of information for sources previously not detected by SASS;
5) generation of light curves for all detected sources found in the HRI.

These products and tools will be generated during phase 2 of the RRA
development.
Present plans call for phase 2 to start some months after phase 1.